With the banking app, if it has an app,, it has a web portal, and that probably has a way of messaging the bank. Let them know which make and model phone you have, which version of Android you're running, and what problems you're having. (and be prepared to wait a few months for the fix). My banking app crashed when I tried to use my fingerprint to get into it. I notified them a few times, as they tried various fixes. (And this was on Pie, months after it was released, on a Pixel 2 - how much more "stock Android" can you get?) It took a few months, but they came out with an update, and it works fine now. (You have updated to the latest version of the banking app, haven't you?)
As for Flash, it has massive security holes, which is why Android dropped support for it. Apple never did support it - Steve Jobs said something to the effect that Flash was designed for exactly the environment that a phone isn't, and he'd never put it on an iPhone. But Dolphin did Flash the last time I looked, and a few others did too. Look for browser in Play, and read the information on each one. (Be aware, though, that by running a browser that handles Flash, you're compromising the security of your phone.)